The present invention relates to a method of electrophotographic printing.
An electric copying machine by way of electrophotography has been widely known in the field of copying technology in which an optical image of an original (a manuscript) of a document or drawing for example, is restored by means of energy of an electro-magnetic radiation beam and a sensitized member.
In the copying machine, a charge latent image corresponding to an optical image of the original is formed on the sensitized member to which a charged photoconductive member is applied and is developed by toner to get a hard copy.
A laser printer also has been widely used in recent years. The laser printer uses a charged photoconductive member as a sensitized member which is scanned by a spot of a laser beam whose intensity is modulated by means of information signals to be recorded to form a charge latent image corresponding to the information signals on the sensitized member. The charge image is developed to obtain a hard copy.
There is further an electrophotographic apparatus to which the copying machine as well as the laser printer are applied.
As is well known, the copying process of an electric copying machine by way of electrophotography is as follows: Firstly, an original optical image is exposed on a sensitized member of a pre-charged photoconductive member to form a charge latent image corresponding to the original optical image thereon.
The charge latent image is then developed by toner and the developed image is transferred onto a transfer paper and is fixed thereon to obtain a hard copy. (The paper needs not be a transfer paper if the paper itself is a sensitized member.)
It is therefore required to two-dimensionally expose an original optical image on a sensitized member of a pre-charged photoconductive material each time in order to obtain a duplicate. Consequently, it is difficult to speed up the copying rate.
It is thus general to obtain many duplicates by means of not a copying machine but a printing machine. In order to solve such a problem, there is an apparatus as a copying machine by way of electrophotography but also doubles as a printing machine disclosed in U.S. Pat. No. 2,576,047.
The apparatus disclosed in the US patent employs zinc oxide as a pre-charged photoconductive material as a sensitized member. When the apparatus operates in printing mode, an original optical image is exposed on a sensitized member to form a charge latent image corresponding to the original optical image thereon.
The charge latent image is then developed by toner to .obtain a fixed image as a master. The master is charged and exposed entirely and is further developed by toner. The developed image is transferred onto a transfer paper and is fixed thereon to obtain a duplicate.
It is essential for companies active in an information-oriented society to document information selected from much information and to deliver the documents to sections in the companies which need that information as soon as possible.
It is therefore required for the documenting mentioned above to duplicate an original by a copying machine, to document the original by a word processor and to obtain many duplicates by copying operation of a copying machine or printing operation of a printing machine.
With an improvement of functions of an electric copying machine, particularly its copying rate, companies have not ordered a printing office but have duplicated documents by themselves with their copying machines if the number of copies is not great.
However, as already mentioned, it is difficult to speed up the copying rate so that a printing machine must be used instead of a copying machine if so many documents.
An apparatus which operates as a copying machine but also doubles as a printing machine by way of electrophotography is useful under such circumastances.
However, the apparatus disclosed in U.S. Pat. No. 2,576,047 already mentioned needs troublesome operation to detach a master used in the printing mode from the apparatus and to install a new sensitized member therein when the printing mode is switched to the copying mode. The apparatus also cannot operate as a laser printer.